Since attempts to control and eliminate malaria parasites have not been successful, the need for developing a vaccine has become increasingly inportant. Individuals living in endemic areas may acquire immunity, but neither the immune mechanism(s) leading to protection nor the antigens involved are known. Antigens associated with the merozoite stage may be of particular relevance, since this asexual stage of the parasite is continuously invading erythrocytes and would be susceptible to immune regulation when extracellular. Recently, I have produced 18 hybridoma cell lines that secrete monoclonal antibodies specific for merozoites of the rodent malaria parasite, Plasmodium yoelii. I propose to purified these antigens by monoclonal antibody-column affinity chromatography and evaluate their immunologic roles in vitro and in vivo. In vitro studies will include incubating purified antigens with functionally different lymphocyte subsets (e.g. B cells, T cells, Lyt-2- and Lyt-2+ cells) and evaluating their effect on antibody secretion and lymphocyte proliferation. In in vivo studies, mice will be injected with purified malarial antigens and resulting humoral and cellular immune responses will be monitored prior to experimental challenge. Thus in vitro and in vivo results can be compared. Since merozites of rodents, primates and man share common antigens, and there are many close parallels between mouse and human immune responses, data from the proposed studies should be relevant toward developing strategies for immunologic intervention in man.